This invention provides an image scanner, which can accurately drive the scanning module or documents based on a stepping control table as well as the method to generate such a table.
Due to the fact that image scanners have been widely adopted in many fields, the resolutions of these scanners are rising continuously under the requirement to promote the quality. For a flatbed scanner, its scanning module is placed at carriage and driven by a driving device which comprising a stepping motor and some guiding mechanics. In order to raise the scanning resolution, the accuracy of the driving device must be raised in the meantime to meet such a high accuracy requirement. However, there are always some tolerance in driving device during manufacture and assembly. The accumulated tolerance will definitely produce some periodic deviations, which make the scanning module fail to be brought to the proper positions accordingly
Reference to FIG. 1. It is a curve to show the deviations generated by a scanning module of an image scanner during scanning. The horizontal axis (x-axis) represents the predefined positions of scanning line and the vertical axis (y-axis) represents the deviation distance for each predefined scanning line. The distances between each scanning line are depending on the resolution of a scanner, for example, {fraction (1/300)} inch for 300 DPI resolution, and is driven by stepping motor with fix steps, for example 8 steps. From the curve 34 in FIG. 1, it can be found that the mechanical tolerance in driving device will produce a periodic deviation during a serial scanning procedure.
This periodic error will cause some variations. For instance, it will make a straight line looks not smooth on image after scanning. Therefore, the main purpose of this invention is to provide a method to move the scanning module accurately based upon a stepping control table in order to solve the problems caused by the periodic deviation.